1) US consumers just got a small standard of living boost. The same things they were buying before, will now cost less. It'll have little to no effect on US domestic manufacturing.
2) This will put some downward pressure on US consumer prices. Giving the Fed even less inflation concern (at least from the CPI angle).
3) The Fed is very, very unlikely to raise interest rates in September. It's practically guaranteed not to happen. Investors are likely to bet on this today, and stocks will probably climb significantly over the next few months in response to the Fed not hiking. The bet will shift from expecting a hike, to not expecting one for the remainder of 2015.
4) This will add fuel to the currency wars. The Eurozone, Japan and others will probably respond. It'll also put pressure on emerging market competitors, from Brazil to Vietnam.
5) It's going to squeeze some Chinese companies carrying debt in other currencies (Bloomberg reports that Chinese companies have $529 billion in dollar and euro based bonds and loans outstanding).
6) The dramatic capital flight out of China over the course of 2015 ($300+ billion so far), will increase.